Horn problems

[DrLadybug]

Please help! I’ve wired my horn in but when I try to mount it to the frame it closes the circuit and starts honking. I’ve tried to insulate it with rubber and the button works, but when it jostles while driving it randomly makes contact and honks. Any ideas out there?

 

[Mike Peters]

See the double copper clip at the base of the motor where you attach the two horn wires on either side of it? That has to be electrically isolated from the body of the horn. If that clip is making contact with the horn body, it will run the horn motor when you attach it to the light bar. As you say, completing the circuit.

Get your voltmeter out and do a continuity test between the double copper clip and horn body. There should be NO continuity. There should be NO continuity between the tubular rivet and copper clip that holds it in place. The rubber washer under the rivet insulates the clip from the rivet. Try that test and get back to us on your results. Good luck.

 

[Bob C]

Is it a stock horn or aftermarket?

 

[Bill G]

An aftermarket non-original horn may be made to have one side of its circuit through the frame (ground). That is not the case with an original Model A horn. Rather than being grounded to the chassis, the Model A horn gets its ground through the horn button and the hot side is connected to battery all the time.

 

[DrLadybug]

It is aftermarket. I can’t find any wires touching the horn body but haven’t taken it fully apart yet. I don’t have the copper clip to check for continuity.

 

[Bill G]

You will probably need to put a horn relay in series with it, and try to figure a way to mount the relay out of sight. The on-off for the Model A horn comes through ground rather than the hot side. Your horn is made so ground is probably hard wired on one side of the circuit if it is done the way I am thinking it might be.

 

[rotorwrench]

I see a red wire that appears to be attached to the motor frame which would ground the motor through the frame if that is what it is. Some of these aftermarket products may be designed to have power to the motor switched on and off. Model As aren't wired that way. The aftermarket stuff may not even be series motors. You just don't ever know what all is out there until you take the covers off and have a look. There are also shunt wound and compound DC type motors and these are more common in the modern era but are polarity sensitive since they some times need to be reversed for rotation or variable speed control. Permanent magnet motors are also common but they are pretty obvious when you see the magnets in them.

On a true series wound horn motor, both the connections to the motor will be completely isolated from the frame of the horn. One will connect to the power at the generator cut out and the other to the light switch horn connection so that it can be ground controlled by the horn button on the steering wheel. The polarity is not an issue with true series wound motors. This link has information about the different types of DC motors with diagrams.
https://electrical-engineering-portal.com/4-types-of-dc-motors-and-their-characteristics

 

[DrLadybug]

Thank y’all so much! You’re right. Since it’s aftermarket, the horn button wires into the horn body instead of internally. So every time I touch the horn against the car it closes my circuit! My Dad didn’t realize that when he bought the horn for me. I just insulated it with grommets and a piece of rubber for now until I can get a different horn. I can’t thank y’all enough!

 

[Bob Bidonde]

Some reproduction horn cover attachment screws are too long and short onto a brush holder. This will sound the horn when it touches a grounded part of the car..

 

[Stew]

Both of the brush holders should be isolated from the horn frame !

If you look on the Brattons website they show an expanded diagram of the horn. There are fiber washers between the brush holder and the frame and a small rubber cone washer on the screw that isolates the mounting screw that goes into the back of the brush holder. Some people use an 8/32 nylon screw to mount the brush holder.

Good luck